Engines may include crankcase ventilation systems to vent gases out of the crankcase and into an engine intake manifold to provide continual evacuation of gases from inside the crankcase in order to reduce degradation of various engine components in the crankcase. During certain conditions, crankcase ventilation systems may be monitored to identify breaches in the system. For example, a fresh air hose (breather tube) may become disconnected, an oil cap may be off or loose, a dipstick may be out, and/or other seals in the crankcase ventilation system may be broken resulting in degradation of various components included in the crankcase.
Various approaches may be used to monitor crankcase ventilation system integrity. For example, diagnostic blow-by approaches may be used wherein a pressure sensor used in the crankcase and a valve in a PCV fresh air hose are opened and a breach in the system is determined based on resulting changes in crankcase pressure or vacuum. Other approaches may use a combination of pressure sensors positioned at different locations in the crankcase ventilation system to monitor crankcase ventilation system integrity.
However, the inventors herein have recognized potential issues with such approaches. As one example, even with the use of multiple sensors and valves, a breach in the system may not be properly diagnosed. For example, there may be conditions where the pressure or vacuum change estimated by the various pressure sensors does not have sufficient signal to noise ratio to discern a crankcase breach, in particular, a small breach. As another example, the use of multiple sensors and valves adds to system costs and complexity. As still another example, based on the location of the sensor, some combinations of pressure sensors may read substantially the same pressure under certain conditions, leading to an increase in redundancy without an increase in the accuracy of the diagnostic routine.
In one approach, to at least partially address these issues, a method for an engine is provided. The method comprises, during engine cranking, while manifold airflow is lower than a threshold, increasing throttle opening, and indicating crankcase ventilation system degradation based on a change in crankcase vent tube pressure following the throttle opening. In this way, a signal used to detect a crankcase breach can be enhanced, allowing even small breaches to be better detected.
In one example, an engine crankcase ventilation system may include a crankcase vent tube coupled between an air intake passage and a crankcase. A pressure sensor (or flow sensor) may be positioned within the crankcase vent tube for providing an estimate of flow or pressure of air flowing through the vent tube. During engine cranking, before fuel is injected into any engine cylinder and while an air flow through the vent tube is low, a controller may determine if there is sufficient intake manifold vacuum for performing crankcase ventilation system breach diagnostics. If there is insufficient intake manifold vacuum (e.g., manifold vacuum is less than a threshold), the controller may increase opening of an intake throttle to enhance the intake manifold vacuum. Alternatively, the controller may open (or increase opening of) a PCV valve coupled between the crankcase and the engine intake manifold to enhance the manifold vacuum. For example, the PCV valve or the throttle may be held open to maintain manifold vacuum at a threshold level for the duration of the diagnostics.
Once sufficient vacuum has been generated, the controller may determine crankcase ventilation system degradation based on characteristics (e.g., amplitude) of a transient dip in pressure sensed by the crankcase vent tube pressure sensor following the throttle opening, during the engine cranking. For example, in response to an amplitude of the transient dip being smaller than a threshold (e.g., a substantially negligible transient dip in crankcase vent tube pressure), a controller may infer that flow through the vent tube is disrupted due to a breach in the integrity of the crankcase ventilation system (such as, due to the crankcase vent tube getting disconnected). Additionally, or optionally, while holding the intake manifold vacuum, the controller may determine crankcase system breach based on differences between an estimated flow rate through the crankcase vent tube relative to an expected flow rate through the crankcase vent tube. Following determination of crankcase system degradation, a mitigating action may be performed, such as the setting of an appropriate diagnostic code while limiting engine speed or load, so as to delay depletion of lubricant from the breached crankcase and aspiration of lubricant from the crankcase into engine components.
In this way, adjustments to a throttle and/or PCV valve can be advantageously used to enhance intake manifold vacuum during engine cranking, thereby improving accuracy of crankcase breach detection. By using existing crankcase ventilation system sensors to diagnose crankcase breach during cranking, a number of sensors and valves employed in a crankcase ventilation monitoring system may be reduced, providing cost and complexity reduction benefits. In addition, the approach enables the crankcase ventilation system to remain active during a diagnostic procedure.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.